1. Field of the Invention
The present invention relates to hydrocyclones in which liquid suspensions of solids, particularly fiber suspensions, can be divided into different fractions by using centrifugal force.
2. Description of the Prior Art
Hydrocyclones are commonly used in the cellulose and paper industry for separating pure fiber material from a fiber suspension which also contains harmful impurities and coarser particles which must be removed before the fiber suspension can be fed to the paper machine. A hydrocyclone comprises a separation chamber the base of which has been provided with a guide channel or channels for the liquid suspension which is to be fed in. This liquid suspension enters the separation chamber tangentially and travels from one end of the chamber to the other vertically. The apex of the separation chamber is open and the impurities which constitute the reject fraction are removed through it. The fiber suspension from which impurities have been removed is for its part removed through a pipe or channel in the base part of the separation chamber; the purpose of this pipe or channel is to receive an inner vortex produced in the separation chamber and containing the pure fiber fraction usable for paper pulp. The former fraction is called the reject fraction and the latter the accept fraction, and the respective parts in the separation chamber are called the reject end and the accept end.
The reason for the decrease in the classification efficency of a hydrocyclone is known to lie in the accept end, where counterflows are produced at the fiber suspension inlet; these flows travel along the outer surface of the accept-receiving pipe towards its inlet end, where a portion of the counterflows is drawn into the accept pipe and is removed along with the fraction usable for paper pulp before it has been possible for the hydrocyclone to separate the impurities which should pass into the reject fraction.